Deoxyribonucleic acid (DNA) is a molecule present in all living organisms, and it contains information about the biological order of the organism to which it belongs. Each distinct living organism has a unique DNA structure, and the structure of the DNA largely determines the biological and physical make-up of each living organism. Knowing details about the structure of DNA molecules interests the scientific, medical, and criminal justice communities, because such detailed information can provide insight into biophysical functions, clues about ailments common to organisms and their cures, and the unique identity of one organism.
The DNA molecule has been well studied and is know to have the form of a double-helix strand comprising at least thousands of paired nucleotides spaced along the strand with a distance of about three nanometers between each pair. The paired nucleotides are present in the DNA in only four types, and are commonly identified by the letters A, C, G, and T. These four letters represent four molecules-adenine, cytosine, guanine, and thymine-belonging to a phosphate group which comprise the DNA. The specific order, or sequence, of these nucleotides along a DNA strand is frequently unknown, and is difficult to determine because of their shear number, submicroscopic size and spacing. Additionally, in a relaxed configuration the long DNA strand coils into a ball-like shape. It is the DNA sequence, also referred to as genetic code, that most interests the scientific, medical, and criminal justice communities.